Watercraft for shallow waters have small draught and, therefore, are sensitive to weight and displacement changes, in particular if channels or tunnels are provided in the body of the ship for guiding the water of the drive mechanism. Moreover, such crafts are easily maneuverable. What is difficult is that such crafts are much endangered by ground contact.
According to the findings of the inventor it is not sufficient that the drive mechanism be protectively installed, in particular against ground contact. That is, the water sucking task must function even during the least drought of the watercraft. These conditions have the result that the centrifugal pump itself is endangered by dirt sucked in with the water.
It is actually known to provide a filter or screen at the water-intake opening to protect the drive mechanism. Such devices, however, are not perfect. Either the filter or screen have a narrow mesh, then the dirt is more or less satisfactorily kept out, however, the efficiency of the centrifugal pump drops off, in particular if this protective device clogs up. If the mesh is wide, then the efficiency is initially better, however, the dirt is not satisfactorily kept out.
The basic purpose of the invention is to make the centrifugal pump itself insensitive with respect to the dirt, in order to be able to avoid the known protective devices either altogether or to construct them with a wide mesh.
A ring is actually damaging to the efficiency of the centrifugal pump. However, the inventor has observed that the efficiency in the known construction drops off significantly in time. This was due to the fact that stones and the like carried with the water would bend the blades of the centrifugal pump or would damage these in another way, which would influence their function. Because of the ring according to the invention, the rotor of the centrifugal pump keeps its shape and assures a constant conveyance, that is a constant efficiency.
Thus the invention permits a safe arrangement of the centrifugal pump.
Since the drive mechanism according to the invention permits stones or the like to be moved with the water, which stones or the like can influence the quietness of the drive, which in turn can afect the control mechanism, that is the controlling of the swivel motion of the elbow, a driving of the elbow by a motor through a self-locking worm gearing is advantageous.
The above-described entire combination permits a very compact construction, which is achieved with an eccentrically disposed swivel axis of the elbow.
Further advantages and characteristics of the invention can be taken from the following description.